1. Field of the Invention
The present invention relates to a display device and a method of driving the display device, and more particularly, to a display device eliminating life-span deviation due to differences between light emitting materials and to a method for driving the display device.
2. Description of the Related Art
A display device forms variable visual display images of moving or still objects based upon its reception of a video signal. The demands of consumers and original equipment manufacturers necessitate a substantial reduction in both the weight and thickness of the display device. Display devices must be reduced in both of weight and thickness in order to be compatible with the renewed slimness of such sources of the video signal as a personal computer or a television, etc. In response to these demands, a display device employing an organic light emitting diode (OLED) has been developed. An OLED is a light emitting diode (LED) whose emissive electroluminescent layer is composed of a film of organic compounds. Therefore, the display device including an OLED uses different technology compared to cathode ray tubes (CRTs), flat panel type display devices such as liquid crystal display (LCD) devices and plasma display panels (PDPs).
In an OLED display device, target data displays a target image having a contour such as an image of a person, and background data displays a background image within which the target image is positioned. When the difference in luminance between the target data and background data is not significant, the outline of the target image may become indistinct from the background image, and thus images on a screen become unclear and less than readily discernable to an audience of human beings.
Therefore, a method for emphasizing the contour of the target image was developed in order to clearly display a border between the target image and the background image. In order to emphasize the contour of the target image, a higher voltage or current should be applied to the display elements corresponding to the contour formed by those pixels defining a transition between the background and the target images, in comparison to the voltage or current applied on other display elements.
In this scenario, it is very important to observe that the life span of an OLED driven by an electrical current, is determined by the magnitude of the electrical current. Particularly, when the magnitude of the electrical current flowing through an OLED increases, the life-span of the OLED decreases. An OLED generally includes several different light emitting materials that emit light of different colors, and the life-spans of light emitting material are different according to the different display color. Therefore, in order to emphasize the contour of the target image, when the electrical current with a large magnitude flows through the OLED, a life span deviation due to different light emitting materials emitting light of different colors may be disadvantageously increased and thus a life-span of a pixel that displays a specific color positioned among pixels that display a plurality of colors may be shortened, thus deleteriously reducing the overall quality. Therefore, the life-span of the OLED display device may be shortened.
The above information disclosed in this Background discussion is only for enhancement of understanding of the background of the present invention and therefore it may contain information that does not constitute prior art that is already known in this country to a person of ordinary skill in the art.